1. Field
The following description relates generally to an organic light emitting diode (OLED) display. More particularly, it relates to generally to an organic light emitting diode (OLED) display with reduced defects.
2. Description of Related Art
An organic light emitting diode (OLED) display is a self emissive display device that displays images with organic light emitting diodes. The OLED display differs from a liquid crystal display (LCD) in that it does not require a separate light source and typically is thinner and lighter than a comparable LCD. Further, the OLED display has desirable characteristics such as low power consumption, high luminance, and high reaction speed, and is gaining more and more attention as a next-generation display device for portable electronic devices.
The OLED usually includes a hole injection electrode, an organic emission layer, and an electron injection electrode. The OLED emits light by energy that is generated when excitons (which are formed by coupling of holes that are received from the hole injection electrode and electrons that are received from the electron injection electrode) within the organic emission layer drop to a ground state.
In order to improve light efficiency by effectively extracting light generated from the organic emission layer, a microcavity effect has been used. The microcavity effect uses a theory that light is iteratively reflected by a reflection layer (e.g., a lower electrode layer) and a transflective layer (e.g., an upper electrode layer) that have a predetermined gap (e.g., an optical path length) therebetween, and a strong interference effect occurs between the iteratively reflected light such that light having a specific wavelength is amplified and light having other wavelengths is offset. Accordingly, color reproducibility and luminance are improved.
However, the reflection layer (the lower electrode) and the transflective layer (the upper electrode layer) generating the resonance have different effective lengths. To compensate for the differences of the effective lengths, a red pixel includes a red emission layer and a red assistance layer, and a green pixel includes a green emission layer and a green assistance layer. Accordingly, when forming the organic emission layer in each pixel, a fine metal mask to deposit each color of the corresponding pixel is required. By the formation of the red assistance layer and the green assistance layer, the number of uses of the fine metal mask is increased. In addition, a blue pixel includes a blue emission layer, and a blue assistance layer may be used for the blue pixel. As the number of uses of the fine metal mask is increased, stain defects and black spots are generated such that the process yield may be deteriorated. Accordingly, there is a need to reduce the number of uses of the fine metal mask.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.